The present invention relates to the field of monoclonal antibodies. In particular, the invention relates to the creation of new biological entities termed triomas and quadromas, which produce new bifunctional antibodies termed recombinant monoclonal antibodies herein. Recombinant monoclonal antibodies (hereinafter designated RMA) have a wide range of diagnostic and therapeutic uses, to be described in detail herein.
Antibodies are normally synthesized by lymphoid cells derived from B lymphocytes of bone marrow. The great diversity of antibody specificities is accomplished by immunoglobulin molecules having many structural features in common. Individual antibody molecules of heterogeneous binding specificity differ in their detailed amino acid sequences and even antibodies of the same specificity are usually a mixture of immunoglobulins having different amino acid sequences, although such sequences may be substantially homologous. The terms "antibody" and "immunoglobulin" are used interchangeably herein.
Individual lymphocytes produce immunoglobulin of a single amino acid sequence. Lymphocytes cannot be directly cultured to produce their specific antibody. However, Kohler, et al, Nature 256, 495 (1975) demonstrated that a process of somatic cell fusion, specifically between a lymphocyte and a myeloma cell, could yield hybrid cells which grow in culture and produce a specific antibody. Myeloma cells are lymphocyte tumor cells which, depending upon the cell strain, frequently produce an antibody themselves, although some "non-producing" strains are known.
The hybrid resulting from somatic fusion of a lymphocyte and a myeloma cell is termed a "hybridoma" cell herein and in the art generally. In a typical fusion procedure, spleen lymphocytes from an animal immunized against a chosen antigen are fused with myeloma cells. The resulting hybridomas are then dispersed in a series of separate culture tubes or microtitre plate wells to screen for cultures producing a desired antibody. Positive cultures are further diluted to obtain colonies arising from a single cell (clones). The clones are again screened for production of the desired antibody. Antibody produced by a cloned hybridoma is termed "monoclonal" herein and in the art.
From genetic studies with lymphocytes and hybridomas, it is known that specific antibodies are coded by DNA segments that are selected from a variety of possible coding segments originally present in germ line cells. As differentiation proceeds, some of the coding segments are rearranged or deleted, so that fully differentiated lymphocytes are genetically restricted to production of a single antibody. See Science 212, 1015 (1981). Previous attempts to demonstrate synthesis of more than one antibody by a single cell or clone have been successful only to the extent that myeloma-myeloma fusion cells have been shown to produce mixed myeloma proteins (Cotton, R. G. H., et al, Nature 244, 42 (1973)).
Monoclonal antibodies are highly specific, being directed against a single antigen only. Furthermore, in contrast to conventional antibody preparations which typically include different antibodies directed against different sets of determinants on the same antigen, monoclonal antibodies are directed only against a single determinant on the antigen. Monoclonal antibodies are useful to improve the selectivity and specificity of diagnostic and analytical assay methods using antigen-antibody binding. A second advantage of monoclonal antibodies is provided by the fact that they are synthesized in pure form by the hybridoma culture, uncontaminated by other immunoglobulins. Monoclonal antibodies may be prepared from supernatants of cultured hybridoma cells or from ascites induced by intraperitoneal inoculation of hybridoma cells into mice.
The immunoglobulin protein structure is well known. Immunoglobulin G (IgG) consists of two heavy protein chains (molecular weight .about.64,000) and two light protein chains (molecular weight .about.22,500). The heavy chains are covalently joined together by disulfide bonds and each light chain is joined to a heavy chain by disulfide bonds. IgM is characterized by the same basic structure as IgG, in multimeric form. Myeloma cells frequently secrete light chain monomers or dimers, sometimes termed myeloma proteins or Bence-Jones proteins, some of which have capacity to bind an antigen. The light and heavy chains of normal antigens are synthesized by the general mechanisms of protein synthesis in cells. The heavy and light chains are separately synthesized and subsequently joined together.
Chemical reassortment of antibody chains has been attempted in the prior art. Early attempts by Stevenson, G. T., et al (Biochem.J. 108, 375 (1968)), yielded only a minor proportion of heterologous associations. More recently, Peabody, D. S., et al, Biochemistry 19, 2827 (1980) demonstrated specific heterologous association of light chains from different myeloma sources. The hybrid molecules showed binding affinity for a ligand which one, but not both, of the parent molecules could bind. Heterologous association of heavy with light chains, or of heavy-light pairs, was not reported. Raso, V., Cancer Res. 41, 2073 (1981) has reported construction in vitro of antibody fragments (F(ab').sub.2 fragments) with binding affinity for two ligands. The reported procedure required partial degradation of the antibody molecules with a pepsin prior to reassortment of the fragments, such that the resulting dual-specificity binding proteins were fragments of antibody molecules.
The use of monoclonal antibodies for a variety of therapeutic purposes has been suggested. A particularly attractive application is for specifically targeted delivery of drugs to specific tissues or cell types, including tumors. For example, Gulliland, et al, Proc. Nat. Acad. Sci. USA, 77, 4539 (1980) have reported making chemical conjugates of a monoclonal tumor antibody with diphtheria toxin. The specific binding of the monoclonal antibody to the target cells makes it possible to deliver a specific drug, inhibitor or toxin to the desired cells while minimizing any interaction with other cells. Such techniques have depended upon chemical coupling reactions to conjugate the drug or toxin with the monoclonal antibody, with attendant disadvantages of loss of activity, reduced specificity and potential unwanted side reactions. Therefore it would be greatly advantageous to provide a targeted delivery system useful in conjunction with agents which need not be chemically coupled to an antibody molecule.